In recent years, attention has been focused on the development of thinning a wafer as the demand for further integrating an IC chip and shrinking its package is increasing. If a wafer is thinned to a certain extent, a deflection occurs on the entire surface with degradation in the strength of a surface, and the wafer must be supported by another support member when being handled. Accordingly, a wafer to be thinned to a certain extent is handled after the strength of the surface is reinforced by being pasted with a support plate made of glass, a nickel-iron alloy, or the like in advance as the support member. The pasting of the support plate to the wafer is made by interposing a substance having an adhesive property (such as an adhesive agent, etc.) between the wafer and the support plate. Moreover, peeling of the support plate from the wafer is made by dissolving the above described substance with a solvent. This solvent is guided to the above described substance by immersing the wafer and the support plate within the solvent.
In recent years, a support plate on which many minute penetration holes for guiding the solvent between the wafer and the support plate are provided in the thickness direction of the support plate, namely, a perforated support plate is widely used as the above described support plate in order to make the solvent react with the above described substance in a short time. The penetration holes are sometimes structured to be unopened so that a glass substance is partially left to be opened later especially on a glass support plate. Such many penetration holes are arranged on the support plate almost evenly with high density over the entire range to which the wafer is pasted.
A configuration of the support plate that is made of an iron-nickel alloy and includes penetration holes is disclosed by Patent Document 1.    Patent Document 1: Japanese Laid-open Patent Publication No. 2005-191550To reinforce the strength of the surface of the wafer to be thinned, a glass support plate of 0.7 mm in thickness is used.
For the above described glass support plate of 0.7 mm in thickness, on which many penetration holes for running a solvent are arranged, all the penetration holes are evenly arranged at a high density within the entire area except for the edge of the perforated support plate and its neighboring area. Accordingly, the solvent is efficiently guided to the entire surface pasted to the wafer through the penetration holes, and the substance having the adhesive property interposed between the wafer and the perforated support plate may be made to quickly react so as to peel the support plate from the wafer in a short time.
In recent years, however, the diameter of a perforated support plate has been demanded to increase to 300 mm or more as the diameter of a wafer is increasing to 300 mm or more. Compared with a general support plate that does not include penetration holes for running a solvent, the perforated support plate is lacking in a substance configuring a base material by an amount corresponding to the penetration holes, leading to a low rigidity. For conventional support plates of small diameters, a certain degree of strength can be secured. However, for perforated support plates of 300 mm or more in diameter and 0.7 mm in thickness, the above described certain degree of strength cannot be secured due to the lack of rigidity, leading to a deflection. Namely, the conventional perforated support plates cannot prevent a wafer from deflecting if it increases in diameter and deflects.
To avoid the above described problem, a support plate processed by thinning a glass plate base material of 1 mm in thickness to be 0.8 mm is conventionally used as a perforated support plate of a large diameter of 300 mm or more. In such a case, however, a plate base material of 1 mm in thickness must be shaved to 0.8 mm. Therefore, the number of process steps increases in comparison with the case where the glass plate base material of 0.7 mm in thickness is used unchanged.
Moreover, the thickness of a perforated support plate of a large diameter of 300 mm or more is different from that of a perforated support plate of a smaller diameter. Accordingly, components for respective thicknesses must be provided to handle perforated support plates of different thicknesses for each device handling perforated support plates (such as a pasting device, a peeling device, etc.), leading to an increase in the number of components or the size of the device.